1. Field of the Invention
The present invention relates to a motor controller for controlling rotation of a motor. More particularly, the present invention relates to a motor controller suitable for the remote radio control of a motor.
2. Description of the Prior Art
Conventionally, motor controllers for controlling motors mounted on controlled equipment in response to control signals transmitted from a transmitter have been developed in hobby and industrial fields.
In motor controllers used for hobby-level radio controllers, the drive frequency of the motor drive signal is generally set to a fixed value. In the recent year, motor controllers that can set the drive frequency to different values have been developed as disclosed in the Japanese Patent Publication No. 6-312065.
However, the motor controller disclosed in the Japanese Patent Publication No. 6-312065 is disadvantageous in that the drive frequency cannot be changed in the course of controlling a controlled unit of model car or model airplane. Thus, the controlled unit cannot be controlled and driven powerfully. Thus, suitable remote control cannot be established in accordance with environmental changes in, for example, a driving course.
In order to solve such a problem, there is proposed a motor controller disclosed in the Japanese Patent Publication No. 2000-51540. In this motor controller, the control lever of the transmitter is manipulated in such a way that the drive signal period is widened so as to set the duty cycle of the drive signal to a smaller value and that the drive signal period is narrowed so as to set the duty cycle of the drive signal to a larger value.
In the prior art, it is possible to achieve a smooth movement of the controlled unit by increasing drive frequency, and a powerful movement thereof by decreasing drive frequency. In this manner, desired remote control in accordance with environmental changes can be established in a certain limited range.
However, the motor controller disclosed in the Japanese Patent Publication No. 2000-51540 is disadvantageous in that the motor mounted on a controlled unit experiences an unexpected heavy load state, and the commutator may burn at lower drive frequencies, if the motor is a high power motor which can output a torque more than a predetermined value. On the other hand, the motor becomes non-powerful, if the motor is a low power motor which cannot output a torque more than a predetermined value, and is subjected to an unexpected heavy load and driven at higher frequencies.
Accordingly, the conventional motor controller is disadvantageous in that the drive control condition cannot be suitably changed when unexpected load change occurs during the motor drive control.